1. Field of the Invention
The present invention relates to a lightfast colorant and a lightfast ink composition including the same, and more particularly, to a lightfast colorant that is derived by chemically binding a benzophenone derivative to the molecular structure of a conventional colorant, and a lightfast ink composition containing the same.
2. Description of the Related Art
Ink-jet printing, which is a kind of non-impact printing, has the advantages of low noise generation, compared to impact printing, and easy color printing realization, compared to laser beam printing.
There are two types of non-impact printing: continuous ink-jet printing and drop-on-demand (DOD) printing. In continuous ink-jet printing, while ink is continuously discharged, a change in an electromagnetic field is induced to control a direction in which the ink is jetted. DOD printing, in which micro droplets of ink are jetted, includes thermal-bubble ink-jet printing and piezoelectric ink-jet printing. In thermal-bubble ink-jet printing, ink is discharged by a pressure generated by the swelling of bubbles that are generated as the ink is heated. In piezoelectric ink-jet printing, ink is discharged by a pressure generated by using a piezoelectric plate that may be mechanically deformable by electricity.
Recently, a dot-size of ink-jet printers utilized has become smaller, and there has been an increasing need for high-resolution, high-quality prints. Smaller dot-size ink-jet printers require a head having smaller nozzle orifices. However, smaller nozzle orifices are susceptible to being clogged by precipitates, and thus affect the size of ink droplets and the performance of the printer. It is obvious that the composition of the ink affects the clogging of the nozzle orifices. For this reason, a wetting agent is commonly added to the ink-jet ink compositions.
An ink composition for ink-jet printing contains a colorant, a solvent, and an additive. A dye or a pigment may be used as the colorant. However, using a dye as the colorant is limited because it causes a print to have poor lightfast and water-fast properties. When using a pigment as the colorant, a resulting print is more lightfast and water-fast than a print prepared using a dye, but is still susceptible to color change or discoloration when exposed to ultraviolet (UV) light. An additional lightfastness enhancer may be used. However, negative side effects, for example, the clogging of the nozzle orifices by agglomerated ink, the formation of a heterogeneous ink composition, and the like, occur when the lightfastness enhancer is used.
As an example, EP 1006161 A1 discloses an ink composition in which a colorant covered with a polymer that includes UV-absorbing and/or lightfast sites is dispersed. The ink composition that includes such a colorant coated with a UV-absorbing polymer is unstable due to poor dispersion stability of the polymer-coated colorant particles and the weak binding force between the colorant and the polymer.